Also see “is notice by tenant valid”
Surrender by operation of law
An agreement by the landlord and the tenant that the term shall be put an end to, acted upon by the tenant’s quitting the premises and the landlord by some unequivocal act taking possession, amounts to a surrender by operation of law. [Phene v Popplewell (1862) 12 C.B.N.S. 334.] But the giving and acceptance of possession must be unequivocal.
So there was no surrender where:
(a) the landlord accepted the keys “without prejudice” [Re Panther Lead Co.  Ch. 978.] ;
(b) the landlord accepted the keys by mistake [Proudreed v Microgen  1 E.G.L.R. 89.] ;